Compare alpha, beta and gamma radiations in terms of their abilities to…

The idea

This statement asks you to compare three radiations on two features: penetration and ionisation. Alpha radiation is the most ionising but the least penetrating; it is stopped by a few centimetres of air or a sheet of paper. Beta radiation ionises less than alpha but penetrates further; it is stopped by a few millimetres of aluminium. Gamma radiation is the least ionising but the most penetrating; it is reduced but not fully stopped by thick lead or concrete. The pattern to recall is inverse: the more ionising a radiation, the less it penetrates. In a multiple-choice question, check both features for each radiation and reject options that reverse the order or give only one feature.

What earns the marks

• Ranks alpha as the most ionising and least penetrating of the three.
• Ranks gamma as the least ionising and most penetrating of the three.
• Places beta between alpha and gamma for both ionisation and penetration.
• Links penetration to stopping materials such as paper, aluminium and lead.

Common mistakes and how to put them right

• Claims gamma is the most ionising.

  Put it right by ranking alpha as most ionising and gamma as least.

• Says alpha penetrates furthest.

  Put it right by stating alpha is stopped by paper or a few centimetres of air.

• Gives the order for one feature only.

  Put it right by comparing both penetration and ionisation for all three.

Exam tips

• Compare all three radiations on both features before selecting an option.
• Use the inverse pattern: most ionising means least penetrating.
• Recall the stopping materials to check penetration rankings.